Background Although the Thrombolysis in Myocardial Infarction (TIMI) flow grade is a valuable and widely used qualitative measure in angiographic trials, it is limited by its subjective and categorical nature.

Methods and Results In normal patients and patients with acute myocardial infarction (MI) (TIMI 4), the number of cineframes needed for dye to reach standardized distal landmarks was counted to objectively assess an index of coronary blood flow as a continuous variable. The TIMI frame-counting method was reproducible (mean absolute difference between two injections, 4.7±3.9 frames, n=85). In 78 consecutive normal arteries, the left anterior descending coronary artery (LAD) TIMI frame count (36.2±2.6 frames) was 1.7 times longer than the mean of the right coronary artery (20.4±3.0) and circumflex counts (22.2±4.1, P<.001 for either versus LAD). Therefore, the longer LAD frame counts were corrected by dividing by 1.7 to derive the corrected TIMI frame count (CTFC). The mean CTFC in culprit arteries 90 minutes after thrombolytic administration followed a continuous unimodal distribution (there were not subpopulations of slow and fast flow) with a mean value of 39.2±20.0 frames, which improved to 31.7±12.9 frames by 18 to 36 hours (P<.001). No correlation existed between improvements in CTFCs and changes in minimum lumen diameter (r=−.05, P=.59). The mean 90-minute CTFC among nonculprit arteries (25.5±9.8) was significantly higher (flow was slower) compared with arteries with normal flow in the absence of acute MI (21.0±3.1, P<.001) but improved to that of normal arteries by 1 day after thrombolysis (21.7±7.1, P=NS).

Conclusions The CTFC is a simple, reproducible, objective, and quantitative index of coronary flow that allows standardization of TIMI flow grades and facilitates comparisons of angiographic end points between trials. Disordered resistance vessel function may account in part for reductions in flow in the early hours after thrombolysis.